SAN FRANCISCO -- Yahoo's user base has grown 20 percent in the last year, CEO Marissa Mayer said today.

During an onstage TechCrunch Disrupt "fireside chat" with TechCrunch founder Michael Arrington, Mayer, who took over as Yahoo's CEO last year, said the company has just passed 800 million monthly active users and that most of the company's recent growth -- which doesn't include users and traffic from Yahoo's acquisition of Tumblr -- has come because of mobile users. The company claims 350 million monthly active mobile users.

Arrington pointed out that Yahoo's stock has nearly doubled since Mayer took over the company's top job, adding about $14 billion in stock value. Mayer said that while some of that growth has been because of smart investments by her predecessors, such as former CEO Jerry Yang's investment in the Chinese search firm Alibaba, much has also been because of the company's new focus on four things: hiring the right people, growing traffic, releasing great products, and boosting revenue.

As a result of that focus, Yahoo's revenue is up, albeit just 1 percent, Mayer said.

Mayer also talked about other evidence that Yahoo has regained the mojo that once made it an Internet powerhouse. For example, she said, the company now gets about 12,000 job applications a week, roughly equal to one for every current Yahoo employee. As well, she said, about 10 percent of the company's hires over the last year have been what she called "boomerangs": former Yahoo employees being brought back into the fold.

That number is impressive, given that over the last few years, as Yahoo's products stagnated, it suffered through numerous leadership changes, and employees raced to leave for jobs at places like Google, Facebook, and Twitter. Few could have predicted that so many former Yahoo people would choose to return so soon after Mayer took the helm.

Touting Yahoo's longtime strength in applications like mail, finance, sports, and news, Mayer added later in the interview that those types of tools present natural growth opportunities in mobile, since those are all things that people like to check on their phones.

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